Conventionally, such a printing apparatus has been known widely that forms an image such as a photograph of face and character information on a printing medium such as a plastic card. This type of printing apparatus uses a direct printing scheme for directly forming an image on a recording medium with a thermal head via an ink ribbon, or uses an indirect printing scheme for forming an image (mirror image) on a transfer film with a thermal head via an ink ribbon, and next transferring the image formed on the transfer film to a recording medium.
Generally, in the case of performing printing processing using a thermal head, in order to reduce the capacity of power supply voltage, reserve stability (prevent a voltage drop) of power supply voltage, reduce the size of the thermal head, etc., the current passage start timing is provided with a time difference so that the passage of current for each strobe applied (input) to the thermal head does not coincide with each other. Each heater element of the thermal head is comprised of a resistor, and the current (energy amount) passing through each heater resistor is of I(current)=V(voltage)/R(resistance). Further, a voltage drop occurs in the power supply voltage due to a large current in passing the current through the thermal head.
For example, Patent Document 1 discloses techniques for providing a heating period and a non-heating period, dividing the period into the side closer to the start and the side closer to the end of a printing cycle, keeping the temperature for a chopping current passage period closer to the end during a heating time closer to the start, and thereby reducing withstand voltage or withstand capacity to improve printing speed.
In other words, in the techniques of Patent Document 1, as shown in FIG. 21, with respect to printing processing of the first printing line, at time t1 a first strobe signal STB1 is switched from an OFF state to an ON state, at time t2 the first strobe signal STB1 is switched to the OFF state, while a second strobe signal STB2 is switched from an OFF state to an ON state, at time t3 the second strobe signal STB2 is switched to the OFF state, the same current passage control is performed on the printing processing of the second and subsequent printing lines, the passage of current through the heater elements with the first strobe signal STB1 and second strobe signal STB2 is not performed at the same time, and the energy amount is thereby suppressed to reduce withstand capacity.